1. Field of the Invention
This invention relates to a method in which the image information on an original film such as a negative film (which is hereinafter sometimes referred to as an "original") is divided into a plurality of pixels which are subjected to photometry and the main area of said original is designated, with the image information on said original being recorded on a light-sensitive material under appropriate conditions of exposure. This method is applicable not only to printers (e.g., a photographic printing apparatus) but also to user friendly copiers. The present invention also relates to a printer (e.g., a photographic printing apparatus), in particular, an enlarging printer, as well as to a user friendly copier, in particular, a copier capable of enlargement, which require only one test printing for permitting the image information on an original to be recorded enlarged under appropriate conditions of exposure.
2. Description of the Prior Art
In photographic printing, the amount of exposure is conventionally controlled in accordance with the large-area transmittance density (hereinafter abbreviated as "LATD") of an original. This LATD method which uses the transmittance density as averaged for the greater part of the area of the original is capable of determining the appropriate amount of exposure for "normal negatives", or negative films that are balanced in terms of both density and color. However, such normal negative assume only about 60% of all the negatives handled by users and the remaining 40% are negatives having scenes that are not balanced in density or color, as exemplified by negatives having a higher or lower density in the background than in the image area or negatives in which, certain colors occupy the greater part of the area.
If the LATD method is applied to such negatives that are not balanced in density or color, subject failures such as density failure or color failure often occur in the scenes that are unbalanced in density or color. With a view to dealing with these subject failures, methods and apparatuses for photographic printing have been proposed, in which a plurality of points on an original are subjected to photometry with an image sensor and average transmittance density, maximum density, minimum density, contrast and other parameters are determined for various areas, such as the upper half area, lower half area and the central area, of the original on the basis of the photometric values on those points, and the amount of correction is calculated from those characteristic values, and the amount of exposure as determined on the basis of LATD is corrected by the calculated amount of correction (see, for example, Japanese Patent Application (kokai) Nos. 23936/1977, 23938/1977 and 28131/1979).
Another method that has been proposed to achieve precise exposure control by dealing with subject failures is a "main area designation method" in which the main area of an original such as the face of a human figure, the human figure itself, and animal or a flower is designated and subjected to photometry with a suitable device such as an image sensor and the resulting photometric values are used independently or combined with the average transmittance density or LATD of the whole original to perform exposure control. This "main area designation method" is incorporated in the system described in Japanese Patent Publication No. 29412/1980 and in the system described in commonly assigned Japanese Patent Application (kokai) No. 232441/1986.
A photographic printer with a simulator is also known as a means of reducing or eliminating N.G. prints; in this type of printer, a simulated image of a finished print that is produced by processing the original with an imaging device is displayed on a monitor using a display device such as a CRT. To optimize the quality of finished print, the amount of exposure is corrected manually by the user who manipulates correction keys on the basis of the color balance and density of the simulated image.
However, the conditions of exposure determined by the methods described above are insufficient to obtain high-quality image, in such cases as enlargement from negative films where enhanced optimization of color and density is required. It has therefore been necessary for a skilled operator to examine the negative film and conduct multiple runs of test printing under the conditions estimated as a result of examination, to thereby determine appropriate conditions of exposure.
According to the method described in Japanese Patent Publication No. 29412/1980, supra, the average density A, maximum density X and contrast .DELTA. are determined as characteristic values for the main area of an original, and a correction signal F is determined by: EQU F=K.sub.1 (-A)+K.sub.2 (X)+K.sub.3 (.DELTA.)
(where K.sub.1, K.sub.2 and K.sub.3 are constants), and this correction signal F is used either independently or combined with a signal indicating the average transmittance density of the whole original to perform exposure control. However, a plurality of characteristic values must be determined even for the main area of the original and, furthermore, a plurality of associated coefficients must be determined empirically and statistically, whereby the precision of determining the appropriate amount of exposure is lowered.
The method described in commonly assigned Japanese Patent Application (kokai) No. 232441/1986, supra comprises the following steps: dividing the image area of an original film into a plurality of sub-areas; obtaining image information for each sub-area; by means of the methods described in Japanese Patent Application (kokai) Nos. 23936/1977, 23938/1977 and 28131/1979, supra, which are intended to determine an amount of exposure that is appropriate for each divided scene on the basis of the obtained image information on that scene, determining the amount of LATD-associated automatic correction of exposure DC as: EQU DC=a.sub.1 D.sub.a +b.sub.1 D.sub.max +c.sub.1 D.sub.min +d.sub.1
(where Da is the LATD of the image area, Dmax is the maximum density of the divided scenes, Dmin is the minimum density of the divided scenes, and a.sub.1, b.sub.1, c.sub.1 and d.sub.1 are constants); further designating a limited area as the main area including the marginal portion that is referenced to a pointer such as the principal subject; determining the amount of correction CR in that area as: EQU CR=a.sub.2 D.sub.a +b.sub.2 D.sub.max +c.sub.2 D.sub.min +d.sub.2
(where a.sub.2, b.sub.2, c.sub.2 and d.sub.2 are constants); and determining the appropriate corrected amount of exposure DC' from: EQU DC'=K.sub.i DC+K.sub.j CR
(where k.sub.i and K.sub.j are constants).
However, this method which uses a number of coefficients involves complicated procedures of calculation and processing; further, the constants a.sub.1 -d.sub.1 and a.sub.2 -d.sub.2 are determined empirically and statistically, and K.sub.i and K.sub.j must also be determined empirically and statistically on the basis of the number of pixels into which the image area of the original is divided, whereby the precision of determining the appropriate amount of exposure is lowered.
As mentioned above, functions comprising a number of characteristic values and coefficients are necessary to determine the appropriate amount of exposure by the prior art methods and this inevitably makes the overall procedures of calculation and processing complicated. Further, the many coefficients involved are determined empirically and statistically and the determined amount of exposure does not have sufficient precision to be applicable to enlarged printing. Hence, it has not been used as the basic amount of exposure for test printing.
Under these circumstances, in order to print a negative film, say, a 35-mm film enlarged onto a light-sensitive material of a larger size, say, a cabinet size, 8.times.10" size, 10.times.12" size, 14.times.17" size or 18.times.22" size, many runs of test printing are conducted until an appropriate amount of exposure is found, with manual correction being performed after each run. This procedure is cumbersome and is not easy to accomplish even by skilled operators. This problem is particularly serious with image recording apparatus of a type that is often operated by many unspecified laymen or beginners, such as copiers that are capable of enlarged duplication of transmission originals such as negative films. If the operator is an unskilled layman, he is not always capable of obtaining an appropriately enlarged image as a result of repeated test printing with such image recording apparatus.